Hi Ian,
The missing alt Issue 31 [1] is a big issue. When Dan Connolly was
chairing the HTML working group he made it a point to have HTML WG
problems that encompassed the same design space in the same issue and
not scattered in numerous issues/bugs so we didn't lose track of the
real problem.
The point of the change proposal [2] is to address the whole problem
comprehensively. The missing alt Issue is:
"What to do when a reasonable text equivalent is unknown/unavailable?"
WAI CG studied the matter comprehensively for several months last year
and came up with a holistic solution, which entailed a defining set of
text alternatives for the img element that enables automatic
validators to programmatically detect the presence or absence of text
alternatives. Any page that lacks a text alternative for an image by
at least one of the proposed methods has the validator flag an error
and declare the page invalid.
WAI CG didn't provide a lot of rationale in their report but some* the
reasoning behind their solution for requiring such a set (as HTML 4
required alt) is that it:
1. Raises public awareness of Web accessibility in general and aids in
accessibility education in particular [3]. Flagging errors is very
good thing indeed. I know this personally because I use the W3C
HTML/XHTML validator as a web accessibility teaching tool. I have my
students use it in the accessibility classes that I teach to flag
missing text alternatives. One of their first lessons is to validate
HTML on the W3C site to ensure that it is error-free and that they
have indeed examined each image. It makes a BIG impression that text
alternatives are mandatory not just for WCAG but as well for valid
HTML4 and XHTML. It is an undeniable advertisement that it is needed.
It is a *first step* in getting that vital message across.
2. Enables tools to quickly discern where text alternatives are needed
and allows for future improvement. It provides a practical method of
detection and handling.
3. Encourages authors to do the right thing. As you said in Bug 8000,
"we _should_ be calling authors out on this kind of mistake. Just
because people do something doesn't mean we should make it valid -
after all, we made <font> invalid, along with many other things.
Conformance is about trying to advise authors to do the right thing."
- Ian Hickson http://www.w3.org/Bugs/Public/show_bug.cgi?id=8000#c1
4. Helps ensure that images have complete structure. Complete
structure requires both src and text alternatives: src is to sighted
users as text alternatives is to some users with disabilities. Omit
the src attribute and sighted users have no content. Omit text
alternatives and some users with disabilities have no content.
To sum this all up, guidance for conformance checkers for text
alternatives needs to encompass machine testable options (whatever
they end up being). Any page that lacks a text alternative for an
image by at least one of the proposed methods has the validator flag
an error and declare the page invalid. If you do that for HTML WG
Issue 31, it would be great.
SIDE NOTES:
1. It is perfectly fine with me if the "generated" or "missing"
attributes are not created. WAI CG said that they wouldn't oppose
them. But then people using image galleries would not have time to
write text alternatives and their content would be invalid. See the
WAI CG consensus document for details on how to implement their advice
without the "generated" or "missing" the options included.
2. Steve is tasked with writing rationale specifically for the
role="presentation" and aria-labelledby options. [4]
3. Private communication email exceptions are beyond the scope of both
HTML5 and WCAG 2.0 and should be addressed at a policy level rather
than the specification level. The intended recipient isn't always the
actual recipient. The intended recipient may well be able to view
images, but rendering them on a device unable to render images or have
images switched off to save on downloads.
4. The title attribute is not an acceptable text alternative as it's
content is not displayed to the user unless they can use a mouse and
beforehand know the content is there. The content of the image title
attribute is also often not detected by AT by default unless the user
makes an explicit choice in their preferences to announce the
attribute contents. Authors are advised to only use the title
attribute for 'additional information' and not as a full equivalent
alternative. Therefore HTML specification text must be line with WCAG,
and previous authoring practices. [5]
Have a good weekend.
Best Regards.
Laura
[1] http://www.w3.org/html/wg/tracker/issues/31
[2]http://esw.w3.org/topic/HTML/ChangeProposals/ImgElement20090126
[3] http://validator.w3.org/docs/why.html#learning
[4] http://lists.w3.org/Archives/Public/public-html-a11y/2010Jan/0325.html
[5] http://www.w3.org/TR/WCAG20-TECHS/H33.html
* I am not a WAI Working Group member and only attended sporadic
teleconferences on the issue so there may be more rationale.